1. Field of the Invention
The present invention relates to a motor control device, a sheet conveying device, and an image forming apparatus.
2. Description of the Related Art
In an image forming apparatus, many motors including a motor for conveying sheets used in image forming are installed, for example. As a control technique for such a motor, known has been a technique in which a central processing unit (CPU) sends to a motor driver a drive signal such as a pulse width modulation (PWM) signal in accordance with a control voltage applied to the motor and the motor driver drives the motor based on the drive signal.
Normally, no electric current flows through the motor when the motor is not to be driven. However, if some kind of abnormality occurs on the drive signal sent to the motor driver from the CPU, the motor driver may cause a serious damage to the motor as the motor driver attempts to drive the motor at a maximum control voltage, even though it is a time when the motor is not to be driven. Therefore, preventing the erroneous operation during a time when the motor is not to be driven is desired.
As a technique to prevent the erroneous operation during a time when the motor is not to be driven, the technique described in Japanese Patent No. 3889669 has been known, for example. This technique interrupts control power supplies for both isolation circuits of two-division type to switches a driver unit into a state where the motor is not driven, and switches a braking device into a brake operating state, to maintain the motor in a stopped state at a time when the motor is not to be driven.
However, the technique described in Japanese Patent No. 3889669 is configured to bring the braking device into a brake operating state to maintain a stopped state of the motor at a time when the motor is not to be driven, and the scale of apparatus configuration becomes large. Therefore, preventing the erroneous operation during time when the motor is not to be driven more easily is desired.